Heretofore, polyamide resins such as nylon 11, nylon 12 and the like are used in wide-range applications because of high chemical resistance thereof, and are, for example, widely used for various structures such as pipes, hoses, tubes, etc. Recently, from the viewpoint of prevention of environmental pollution, rigorous emission restrictions have been applied, and for example, the above-mentioned various structures for use for fuel oil have become desired to have high barrier properties for the purpose of preventing volatile components such as volatile hydrocarbons and the like from penetrating through the structures to be diffused out in air.
However, various structures formed of polyamide resins, especially nylon 11 or nylon 12 excellent in strength, toughness, chemical resistance and flexibility could not have sufficient barrier properties against volatile hydrocarbons and the like, and improvement thereof is desired. In addition, recently, alcohol gasoline blended with an alcohol such as methanol, ethanol or the like has been being put into practical use, but alcohol gasoline has high permeability and readily vaporizes in air, and therefore the barrier properties thereof must be increased more.
As a means for enhancing the barrier properties, proposed is a multilayer structure having a barrier layer excellent in barrier properties in addition to a polyamide layer composed of nylon 11 or nylon 12. For example, PTL 1 discloses a multilayer structure containing a polyamide layer composed of nylon 11 and/or nylon 12 and a barrier layer composed of nylon 9T.